1. Field of the Invention
The present invention relates generally to conversion and display of image formats.
2. Related Art
Many techniques are used to produce electronic images over various display devices. Electronic images are typically produced by dividing an image into a rectangular array of discrete elements. The number and size of these discrete elements, or pixels, define the image size and resolution to produce various image formats. A wide variety of image formats are used in current electronic equipment. Most display devices are fixed format displays such as CRT monitors, projectors and LCD screens. Image formats such as VGA, SVGA, XGA, SXGA, UXGA and HDTV are common while a multitude of other formats are used in various other displays such as in LCD screens used in portable electronic equipment. Most common display systems are fixed format screens such as UXGA, which is 1600 by 1200 pixels or SXGA, which is 1280 by 1024 pixels. As the number of image formats increases, frequently an input image to such a fixed format screen is different than the available pixels. For example, if a VGA input having 640 horizontal pixels and 480 vertical pixels is displayed on an XGA screen having 1024 horizontal pixels and 768 vertical pixels, 384 horizontal rows and 288 vertical columns of pixels are left unused. The VGA image would only use 60.9% of the entire available XGA screen. The presence of this unused area is undesirable for both efficiency and aesthetic reasons.
Several methods are used in the industry for converting images from one format to another to fully utilize all of the available display area. One simple method is to enlarge each column and row of pixels using various mathematical operations to approximate the pixel values in the final enlarged image. Another approach is to alter the sampling frequency to provide data at the correct pixel spacing using a scan-conversion unit.
Other methods insert blank pixels into an image and then interpolate the value of the blank pixels. The interpolation may be linear and based on the distance that the blank pixel is from the original pixel. Other interpolation methods use various means of interpolating such as using a weighted average of all neighboring pixels or a combination of interpolation schemes based on the surrounding pixels. Such methods may utilize linear, bi-lincar or bi-cubic interpolation schemes to resize images. Linear schemes use a weighted average of the two nearest pixels. Bi-linear interpolation schemes use a weighted average of the four nearest pixels to compute the blank pixel. Bi-cubic interpolation schemes use a weighted average of the nearest sixteen pixels, often calculated using a cubic spline. These interpolation schemes require large numbers of calculations and alter the original image resulting in a reduced contrast in the final image. This is particularly problematic with sharp transitions in signals such as with text and high contrast graphics. The enlarged image resulting from most current interpolation schemes is slightly blurred and has a reduced quality at edges within the image.
The current methods of format conversion generally require some measure of continuing calculations to convert an image. These continuing calculations are often significant enough to degrade the image quality, since the time necessary to create the converted image may exceed the frame rate. This results in either a reduced effective frame rate and/or discontinuous jumps in the image over time. The use of more expensive vector displays allow for variable frame rates, but the resulting image will often contain discontinuities and may create a noticeable flicker at longer frame times. Clearly, if the output format is not an integral multiple of the input format the more computationally intensive calculations create undesirable results in the displayed images and increased complexity. Conversion techniques which avoid excessive calculations and preserve the original image quality is therefore a continuing pursuit in the image display industry.
It has been recognized that it would be advantageous to develop a format conversion method which is passive and eliminates the computational requirements of the prior art.
The present invention provides a passive image format conversion device, which includes: a laser light at a predetermined frequency along a given optical path; a line converter placed in the optical path for converting the laser light to a fan of light; a lens which is moveable with respect to the light source and placed along the optical path within the fan of light and configured to collimate the fan of light; and an array of N light modulators placed in the path of the collimated light column, wherein the moveable lens may be displaced along the optical path to produce a collimated light column of variable image sizes incident on a predetermined portion of the light modulators.
In accordance with a more detailed aspect of the present invention, the system includes an input image signal connected to the array wherein the input image signal has n vertical pixel data over h columns, wherein within each column the n pixel data are modulated on kn light modulators, where n, h and k are positive non-zero integers and kn/N defines the predetermined portion of light modulators and the corresponding variable image size, to produce a modulated light column. In order to produce a two-dimensional image each of the h columns of data may be modulated consecutively over a given time.
In accordance with another more detailed aspect of the present invention, the system includes a movable mirror oriented to reflect the modulated light column toward a projection surface.
In accordance with a yet more detailed aspect of the present invention, the system includes a zoom lens placed along the optical path of the modulated light column after the array and before the projection surface. This zoom lens is adjusted to change the height of the modulated light column to fill the entire vertical pixels of the destination display.
In accordance with another more detailed aspect of the present invention, the line converter is a Powell lens.
In accordance with a more detailed aspect of the present invention, the system includes a laser light source producing a light having a frequency within a range selected from the group consisting of: blue, red and green. The combination of these modulated light frequencies will produce a full color image at a different format than the original.
In accordance with another aspect of the present invention, the laser light sources are pulsed and then combined prior to the line converter. The combined laser light may be a multiplexed light having consecutive intervals of each predetermined frequency.
In accordance with a more detailed aspect of the present invention, each of the N light modulators is a grating light valve device having a primary ribbon and a reference ribbon.